Abstract:

Objective China produces more than 47.6 million tons of waste textiles every year, including 80% of waste polyester and cotton textiles. Whilst the recycling of waste polyester has made progress, the recycling of waste cellulose fabrics is still difficult. In view of the low recycling rate of waste cotton textiles, the difficulty of regeneration and the poor quality of recycled products, a simple and efficient micro-dissolution thermal "welding" process using ionic liquid (IL) for preparing a high-strength all-cellulose degradable hydrophobic "plastic-like" film was proposed.

Method In this research, 1-Butyl-3-methylimidazolium chloride ([BMIM]Cl) was the main solvent for preparing the self-reinforcing all-cellulosic "plastic-like" film material by micro-dissolution thermal "welding". Firstly, the waste cotton fabric was soaked in [BMIM]Cl aqueous solution system, then heated and de-watered to activate the IL to make the cellulose partially dissolve, then the dissolved part was bonded with the undissolved cellulose by hot pressing, and the hydrophobic functionalization of polydimethylsiloxane(PDMS) was carried out simultaneously. The mechanical properties, contact angles and degradation of film were tested, and the structure and properties of the films were further characterized by SEM, XRD and TGA, etc.

Results The all-cellulose degradable hydrophobic "plastic-like" film material prepared from waste cotton fabrics had a smooth and uniform surface. The "plastic-like" film material demonstrated certain plasticity and excellent comprehensive mechanical properties. The microscopic appearance of the partially dissolved cellulose and the undissolved part successfully bonded together by hot press-thermal "welding" were clearly visible. XRD results indicated that the dissolved part of the cellulose of the film material was transformed from cellulose type I to cellulose type II, and the undissolved part still retained part of the cellulose type I structure. The films demonstrated excellent thermal stability, where thermal degradation temperature was shown up to 350 ℃, much higher than the temperature standard used by the industry. The hydrophobic functionalization was finished onto the surface of the film using PDMS. The film had good waterproof performance, and the contact angle was up to 110° and water vapor transmittance was less than 10%, showing excellent hydrophobicity and humidity resistance. The all-cellulose degradable hydrophobic "plastic-like" film material demonstrated better overall resistance in organic chemicals, and certain resistance in inorganic chemicals, but the material should not be used in strong acid and strong oxidation environments. It also had excellent comprehensive properties then some commercial bioplastic materials such as polypropylene(PP) and polylactic acid(PLA), and its mechanical properties, natural degradability and sustainable durability were particularly outstanding.

Conclusion A high-strength all-cellulose degradable hydrophobic "plastic-like" film had been successfully prepared by micro-dissolution thermal "welding" using ionic liquid. The film exhibited excellent mechanical properties, with tensile strength up to 39 MPa, break elongation was 40%. The bending strength was up to 120 MPa, break elongation was more than 5%. It also had good hydrophobicity and moisture resistance, with contact angle up to 110° and water vapor transmittance was less than 10%. In particular, it was completely biodegradable. The degradation rate in 60 days of soil landfill was 85.6%, and it also showed stable heat resistance and chemical resistance. Therefore, this work provided a promising and useful method to the recycling and re-utilization of waste textiles, which was environmentally friendly. Compared with the traditional method of completely dissolving and regenerating cellulose to prepare films, the processing efficiency was higher and the strength protection of raw fiber was better. More importantly, the film prepared by recycling waste cotton fabrics could be used in the packaging field, such as packaging materials and transportation plates, helping to eliminate environmental pollution from the source and achieve sustainable development of the cotton cellulose cycle.

Key words: recycling of waste cotton fabric, ionic liquid, thermal welding, polydimethylsiloxane, biodegradable film material